Conventionally, as a fan clutch device of this type, one of a system is known in which a torque transmission chamber incorporating a drive disk therein is provided in a sealed housing composed of a nonmagnetic case and a cover mounted on the case, the case and the cover being supported via a bearing on a rotary shaft to which the drive disk is fixed; a side wall face of an oil reserving chamber formed by a hollow in the drive disk is provided with at least one oil circulating flow passage hole communicating with a torque transmission gap; a valve member having magnetism for opening or closing the oil circulating flow passage hole is provided; and rotary torque transmission from a drive side to a driven side is controlled by using an electromagnet to actuate the valve member to increase or decrease an effective contact area of oil in a torque transmission gap formed between the drive side and the driven side.
As an external control type fan clutch device of this type, one of a system in which an electromagnet fixed to a rotary shaft side is energized to actuate a valve member via an armature of the valve member mounted on a drive disk, thereby externally controlling opening and closing of a circulating flow passage. The configuration of the device employs a system in which a magnetic flux due to excitation of a coil of the electromagnet is transmitted to the armature of the valve member composed of a leaf spring through a magnetic path of the rotary shaft composed of a highly magnetic permeable magnetic material to make up a magnetic circuit (magnetic loop) for return to the electromagnet again, and then the flow rate of the torque transmission oil is controlled by actuating the valve member within the clutch device using the electromagnet (see U.S. Pat. No. 4,987,986).
The conventional external control type fan clutch device described above has a disadvantage. More particularly, since the magnetic circuit (magnetic loop) is configured utilizing the bearing supporting the electromagnet actuating the valve member on the rotary shaft, there is the problem that the magnetic circuit is too long to efficiently transmit magnetic force of the electromagnet to the armature, excessive electromagnetic force is required in order to attract the armature, the size and weight of the electromagnet is increased, the size and weight of the fan clutch device cannot be reduced, and power consumption is also increased.
The invention has been made to solve the disadvantage of the convention external control type fan clutch device described above, and the object of the invention is to provide an external control type fan clutch device where size reduction and weight reduction, and power saving are achieved in a fan clutch device.